Dolly Parton's Nephew Unloaded in Profanity-Laced Emails Before Estate Fight

Dolly Parton's nephew Bryan Seaver went scorched-earth in a series of emails ... calling one man a "f***ing s***bag loser" and warning his lawyers would "start f***ing you up the ass" ... according to newly filed court docs.

The wild alleged messages, obtained by TMZ, appear to stem from a dispute over security and construction issues at a Nashville property tied to Dolly's estate.

In the emails, Seaver complained about staffing, alleged drug use by subcontractors, and a build-out he claimed was badly behind schedule.

Then came the fireworks ... in one alleged email, he told the man, "Let's play ball you f***ing s***bag loser," before calling him a "worthless skinny fat nerd" and ending with ... "Go f*** yourself you f***ing weakling."

In another, Seaver told him to "wire your balls on and start doing professional work" ... then called him a "f***ing red leg bushwhacking Missouri s*** bag."

As we told you ... Seaver -- Dolly's nephew and longtime head of security -- was recently fired amid a nasty battle with the company managing her estate, and a judge later granted a temporary restraining order against him after allegations of threatening behavior.

Seaver has denied making threats and says his comments have been taken out of context.

He was also the family member selected to announce Dolly's death ... and later bragged about the massive attention that post received.